1. Field of the Invention
This invention pertains to a hybrid electric vehicle (HEV), whose powertrain includes an internal combustion engine (ICE). More particularly, the invention pertains to a HEV, whose engine may be a normally-aspirated stoichiometric or lean-burn ICE, a stoichiometric or lean-burn supercharged ICE, or a stoichiometric or lean-burn turbocharged ICE.
2. Description of the Prior Art
A hybrid electric vehicle (HEV) includes multiple torque sources to produce driver-demanded wheel torque. Prior art relating to HEVs recognize bounds in engine torque and power, but fail to recognize necessary bounds for electrical supplementary power aside from hardware limitations (battery, electronics, and electrical machines). Potential exists for inconsistent vehicle acceleration and inconsistent emissions for HEVs where the various power sources have a significant variation in either or both dynamic torque response and emissions output versus time, such in as turbocharged engines. Such inconsistent vehicle acceleration and emissions in HEVs are possible because of variations in the time to produce torque from multiple power sources having different characteristics.
The inconsistent variation in dynamic response called “turbolag” for turbocharged engines can be reduced in lean burn engines with direct injection schemes, by post injection of fuel in the cylinders of gasoline engines and diesel engines. Such fuel injections, following the main combustion injection, increase exhaust temperature, which keeps the speed of the turbocharger high enough to achieve higher intake manifold pressures when necessary. However, this technique causes significant reduction in fuel economy and exhaust gas emissions penalties.
A need exists to eliminate such inconsistencies when various engine configurations are employed in a HEV powertrain. For example, in stoichiometric turbocharged engine HEV applications, an inconsistent perceived “turbolag” is perceived negatively by the vehicle operator.